The proposed research is intended to answer the questions: (1) What is the nature of the defectiveness of adenovirus replication in monkey cells? (2) What are the mechanisms by which one virus enhances the growth and oncogenicity of another? (3) What portion of the adenovirus and SV40 genomes are responsible for the oncogenicity of these viruses? These questions are to be answered by: (1) Biophysical and immunochemical analysis of the nucleic acid and protein products of defective adenovirus replication in monkey cells, in the presence and absence of SV40 co-infection. (2) Study of the segment of SV40 genome, or product of SV40 replication responsible for overcoming the block to efficient adenovirus replication. (3) Analysis of the adenovirus genome in the adenovirus-SV40 hybrid virus using temperature sensitive (ts) mutants will be carried out. It is hoped that these studies will succeed in isolating and characterizing the oncogenic genome of adenovirus and SV40, and give insight into the nature of defective viral synthesis and host range restriction.